Photosensitive glasses and glass ceramics and composite glass materials made therefrom

ABSTRACT

Photosensitive lithium zinc aluminosilicate glasses that can be selectively irradiated and cerammed to provide patterned regions of glass and lithium-based glass ceramic, and composite glass articles made from such glasses and glass ceramics are provided. Compressive and tensile stress at the interface of the lithium-based glass-ceramic and lithium zinc aluminosilicate glass may be used to frustrate crack propagation in such a composite glass/glass ceramic article. Methods of making composite glass articles comprising such lithium-based glass ceramics and lithium zinc aluminosilicate glasses are also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/413,731 filed on Jan. 24, 2017 which claims the benefit of priorityunder 35 U.S.C. § 119 of U.S. Provisional Application Ser. No.62/287,157 filed on Jan. 26, 2016, the content of which is relied uponand incorporated herein by reference in its entirety.

BACKGROUND

The disclosure relates to photosensitive glass. More particularly, thedisclosure relates to photosensitive glasses that can be treated to formglass ceramics. Even more particularly, the disclosure relates tophotosensitive lithium zinc aluminosilicate glasses and glass ceramicsthat may include both transparent and opaque or translucent (i.e.,opalized) regions.

Glass-ceramics are nominally produced by a thermal process in which theas-made glass is thermally treated to produce a controlled crystallinephase. Cerium and silver photosensitizers have been used in glasssystems, such as FOTOFORM™ and FOTA-LITE™, to produce photosensitivematerials in which the crystal content is well below the 50% level thattypically defines a glass ceramic. In such glass systems, an opal (i.e.,opaque, optically dense, white, light scattering) phase containing NaFis formed in regions of the glass that are exposed to short wavelengthlight followed by heat treatment, while unexposed regions of the glassremain clear.

SUMMARY

Photosensitive lithium zinc aluminosilicate glasses that can beselectively cerammed to provide patterned regions of glass and glassceramic, and composite glass articles made from such glasses and glassceramics are provided. When these glasses are exposed to ultraviolet(UV) radiation and thermally treated (cerammed), a lithium-based glassceramic having a β-quartz crystal structure is formed in selectedregions of the glass. In some embodiments, the lithium zincaluminosilicate glass is “negatively” photosensitive; i.e., alithium-based glass ceramic is formed in the portion of the glass thatis not exposed to, or shielded from, the UV radiation while thetransparent lithium zinc aluminosilicate glass remains in those regionsthat are exposed to the UV radiation. In other embodiments, the lithiumzinc aluminosilicate glass is “positively” photosensitive; i.e., alithium-based glass ceramic is formed in the portion of the glass thatis exposed to the UV radiation while the transparent lithium zincaluminosilicate glass remains in those regions that are not exposed tothe UV radiation. In some embodiments, the lithium-based glass ceramicis “opalized”; i.e., opaque or translucent, or in some embodimentsopalescent. Compressive and tensile stress at the interface of thelithium-based glass-ceramic and lithium zinc aluminosilicate glass maybe used to frustrate to crack propagation in such a compositeglass/glass ceramic article. Methods of making composite glass articlescomprising such lithium-based glass ceramics and lithium zincaluminosilicate glasses are also provided.

Accordingly, one aspect of the disclosure is to provide a compositeglass article comprising a first region and a second region. The firstregion comprises a lithium-based glass ceramic. The lithium-based glassceramic comprises a residual glass phase and a ceramic phase comprisinga lithium aluminosilicate phase having a lithium aluminosilicate stuffedβ-quartz structure. The second region comprises a lithium zincaluminosilicate glass comprising at least one sensitizing agent and atleast one nucleating agent. The lithium zinc aluminosilicate glass isphotosensitive to ultraviolet radiation having a wavelength in a rangefrom about 248 nm to about 360 nm.

A second aspect of the disclosure is to provide a lithium zincaluminosilicate glass comprising at least one sensitizing agent and atleast one nucleating agent, wherein the lithium zinc aluminosilicateglass is photosensitive to radiation having a wavelength in a range fromabout 248 nm to about 360 nm.

A third aspect of the disclosure is to provide a method of making acomposite glass article comprising a lithium zinc aluminosilicate glassand a lithium-based glass ceramic. The lithium-based glass ceramiccomprises a residual glass phase and a ceramic phase, wherein theceramic phase comprises a lithium aluminosilicate phase having a lithiumaluminosilicate β-quartz structure. The method comprises: providing alithium zinc aluminosilicate precursor glass comprising at least onesensitizing agent and at least one nucleating agent, wherein the lithiumzinc aluminosilicate glass is negatively photosensitive; exposing afirst region of the lithium zinc aluminosilicate precursor glass withultraviolet radiation having a wavelength in a range from about 248 nmto about 360 nm, wherein a second region of the lithium zincaluminosilicate glass is unexposed to the ultraviolet radiation; andheating the exposed lithium zinc aluminosilicate precursor glass to formthe lithium-based glass ceramic in the second region.

A fourth aspect of the disclosure is to provide a method of making acomposite glass article comprising a lithium zinc aluminosilicate glassand a lithium-based glass ceramic. The lithium-based glass ceramiccomprises a residual glass phase and a ceramic phase, wherein theceramic phase comprises a lithium aluminosilicate phase having a lithiumaluminosilicate β-quartz structure, and a residual glass phase. Themethod comprises: providing a lithium zinc aluminosilicate precursorglass comprising at least one sensitizing agent and at least onenucleating agent, wherein the lithium zinc aluminosilicate glass ispositively photosensitive; exposing a first region of the lithium zincaluminosilicate precursor glass to ultraviolet radiation having awavelength in a range from about 248 nm to about 360 nm, wherein asecond region of the lithium zinc aluminosilicate precursor glass isunexposed to the ultraviolet radiation; heating the lithium zincaluminosilicate precursor glass at a first temperature for a first timeperiod; and heating the lithium zinc aluminosilicate precursor glass ata second temperature for a second time period to form the lithium-basedglass ceramic in the first region.

These and other aspects, advantages, and salient features will becomeapparent from the following detailed description, the accompanyingdrawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of positively photosensitive lithium zincaluminosilicate precursor glass/glass-ceramic samples in which ZrO₂ wasadded to a negatively photosensitive lithium zinc aluminosilicateprecursor glass composition;

FIG. 2 is an x-ray diffraction pattern obtained for an opalized portionof a sample that was exposed to UV radiation, heat treated first at 575°C. for two hours, cooled to room temperature, and then heat treated at575° C. for two hours;

FIG. 3 is a photograph of two samples following exposure to ultravioletradiation, and heat treatments at a first temperature and a secondtemperature;

FIG. 4 is a photograph of two samples following exposure to ultravioletradiation, and heat treatments at a first temperature and a secondtemperature;

FIG. 5A is a plot of thermal expansion as function of temperature forthe lithium-based glass ceramic of the composite glass article describedherein;

FIG. 5B is a plot of thermal expansion as function of temperature forthe lithium zinc aluminosilicate glass described herein;

FIG. 6 shows a microscopic image of a composite glass article viewedunder non-polarized light (A) and under polarized light (B);

FIG. 7 is a photograph showing the internal stress produced in apatterned composite glass article comprising a positively photosensitivelithium zinc aluminosilicate glass and the lithium-based glass ceramicdescribed herein;

FIG. 8 is a schematic representation of a patterned composite glassarticle described herein;

FIG. 9 is a flow chart describing a method of making a composite glassarticle from a negatively photosensitive lithium zinc aluminosilicateprecursor glass; and

FIG. 10 is a flow chart describing a method of making a composite glassarticle from a positively photosensitive lithium zinc aluminosilicateprecursor glass.

DETAILED DESCRIPTION

In the following description, like reference characters designate likeor corresponding parts throughout the several views shown in thefigures. It is also understood that, unless otherwise specified, termssuch as “top,” “bottom,” “outward,” “inward,” and the like are words ofconvenience and are not to be construed as limiting terms. In addition,whenever a group is described as comprising at least one of a group ofelements and combinations thereof, it is understood that the group maycomprise, consist essentially of, or consist of any number of thoseelements recited, either individually or in combination with each other.Similarly, whenever a group is described as consisting of at least oneof a group of elements or combinations thereof, it is understood thatthe group may consist of any number of those elements recited, eitherindividually or in combination with each other. Unless otherwisespecified, a range of values, when recited, includes both the upper andlower limits of the range as well as any ranges therebetween. As usedherein, the indefinite articles “a,” “an,” and the correspondingdefinite article “the” mean “at least one” or “one or more,” unlessotherwise specified. It also is understood that the various featuresdisclosed in the specification and the drawings can be used in any andall combinations.

As used herein, the terms “composite glass article” and “composite glassceramic articles” are used in their broadest sense to include any objectmade wholly or partly of glass and glass ceramic. Unless otherwisespecified, all compositions are expressed in terms of weight percent (wt%). As used herein, the terms “ceram” and “ceramming” refer to a heattreatment (or heat treatments) or process in which a precursor glass isconverted to a glass-ceramic.

As used herein, the term “glass ceramic” refers to a material comprisinga glass phase and a crystalline ceramic phase, wherein the ceramic phaseaccounts for or comprises at least 50 volume percent of the material.The terms “glass ceramic” and “crystalline” are equivalent terms and maybe used interchangeably herein.

As used herein, the term “opal” refers to an opaque, optically dense,white, and/or light scattering glass, ceramic, or glass ceramic materialthat may, but does not have to, have opalescent properties. The term“opalizing” refers to a process of transforming a glass, ceramic, orglass ceramic material into an opal material. An opal or opalizedmaterial comprises at least one crystalline or ceramic phase in whichthe crystalline particles have a mean particle size that is within orgreater than the wavelength range of visible light (400 nm-750 nm). Asused herein, the term “translucent” refers to a material that transmitsand diffuses light such that objects beyond the material cannot be seenclearly with the unaided eye.

As used herein, the terms “reverse photosensitive,” “negativephotosensitive,” and “negatively photosensitive” refer to a material andprocess whereby a region of the material exposed to electromagneticradiation remains clear, while an unexposed remainder of the materialbecomes opalized or translucent when the material is subsequently heatedat a temperature greater than room temperature. Conversely, the terms“positive photosensitive” and “positively photosensitive” refer to amaterial and process whereby a region of the material exposed toelectromagnetic radiation becomes opalized or translucent, while theunexposed remainder of the material remains clear.

It is noted that the terms “substantially” and “about” may be utilizedherein to represent the inherent degree of uncertainty that may beattributed to any quantitative comparison, value, measurement, or otherrepresentation. These terms are also utilized herein to represent thedegree by which a quantitative representation may vary from a statedreference without resulting in a change in the basic function of thesubject matter at issue. Thus, a glass that is, for example, referred toas being “substantially free of TiO₂” or “free of TiO₂” is one in whichTiO₂ is not actively added or batched into the glass, but may be presentin very small amounts (e.g., ≤100 ppm or, in some embodiments, ≤50 ppm)as a contaminant.

Referring to the drawings in general, it will be understood that theillustrations are for the purpose of describing particular embodimentsand are not intended to limit the disclosure or appended claims thereto.The drawings are not necessarily to scale, and certain features andcertain views of the drawings may be shown exaggerated in scale or inschematic in the interest of clarity and conciseness.

In one aspect, a photosensitive lithium zinc aluminosilicate glass isprovided. The glass comprises at least one sensitizing agent and atleast one nucleating agent. The lithium zinc aluminosilicate glass isphotosensitive to ultraviolet (UV) radiation having a wavelength in arange from about 248 nm to about 360 nm. In some embodiments, the atleast one sensitizing agent may include, but is not limited to, at leastone of silver and cerium. The at least one nucleating agent may include,but is not limited to, silver and/or at least one halogen or halide. Insome embodiments, the at least one nucleating agent comprises at leastone of fluorine, chlorine, and bromine. In particular embodiments, theat least one nucleating agent comprises fluorine and/or bromine.

In some embodiments, the photosensitive lithium zinc aluminosilicateglass is negatively photosensitive; i.e., a region of the materialexposed to ultraviolet radiation and subsequently heat treated orcerammed remains transparent, while the remainder of the material thatis not exposed to, or shielded from, such radiation and is subsequentlyheat treated at a temperature of at least about 500° C. becomes opalizedor translucent. In such embodiments, the photosensitive glass comprisesa nucleating agent and a sensitizing agent such as, but not limited, tofluorine. Silver, which acts as the nucleating agent in the exposedportion of the glass, has a face-centered crystal (FCC) structure with alattice constant of 0.408 nm, whereas LiF has a FCC structure with alattice constant of 0.407 nm. Because the Ag lattice constant closelymatches that of LiF, Ag serves as highly effective nucleating agent forLiF. The multiplicity of these nucleation sites is so great and thenucleation is so prolific that the LiF crystals do not grow to a size atwhich they noticeably scatter light, thus making the exposed regiontransparent. In some embodiments, the crystallites formed in thisexposed region are smaller than the wavelength of visible light (400nm-750 nm). In some embodiments, the crystallites formed in the exposedregion are less than 100 nm in size.

In those regions of the negatively photosensitive lithium zincaluminosilicate glass that are not exposed (also referred to herein as“unexposed”) to such radiation, the silver metal nuclei are not formed.Consequently, crystals of the various ceramic phases may grow to largersizes in those regions of the glass that are not exposed to the UVradiation, in some embodiments rendering these regions opal—i.e., opaqueor, at a minimum, translucent. In some embodiments, the crystallitesformed in this unexposed region are at least as large as the wavelengthof visible light (400 nm-750 nm). In some embodiments, the crystallitesformed in the unexposed region are greater than 1 μm in size. Whenheated at a temperature of at least about 500° C., a lithium-based glassceramic comprising a crystalline ceramic phase and a residual glass isformed in those regions of the glass that are not exposed to suchradiation.

Depending on the heat treatment temperature, the crystalline ceramicphase in the region of the precursor glass that is not exposed to UVradiation comprises lithium aluminosilicate (LAS, or Virgilite), whichhas a β-quartz crystal structure, and lithium fluoride (LiF, orGriceite). The LAS phase may be described as a “stuffed β-quartz” phasein which LiAl₂O₃ occupies SiO₂ sites within the crystal structure. Insome embodiments, LAS is the dominant crystal phase; i.e., LAS comprisesthe majority of the crystalline phases present in the ceramic. Theceramic phase may further comprise LiF. In some embodiments, the LASphase comprises at least about 50 volume percent of the glass ceramic.The lithium zinc aluminosilicate glass is clear and transparent as made,but, in some embodiments, when not exposed to UV radiation in the248-360 nm ranges and heat treated (“cerammed”), opalizes when reheatedto a temperature of at least about 540° C.

At temperatures below about 540° C., LiF is the only crystallizingphase, whereas both LiF and LAS phases crystallize at highertemperatures. Silver metal nucleates the LiF and either silver metal orLiF nucleates the LAS phase. Unexposed regions, however, are devoid ofsilver precipitates, and LiF is presumably the nucleating phase for LASin these regions.

The negatively photosensitive glass and glass ceramic describedhereinabove also comprise fluorine. Fluorine not only providesphotosensitivity, but also ensures extensive nucleation of the crystalphases in the unexposed region of the precursor glass. Without fluorine,the unexposed regions appear to crystallize in an uncontrolled manner,leading to fracture and crumbling of the material at temperatures of550° C. or greater.

When exposed to electromagnetic radiation having a wavelength in a rangefrom about 248 nm to about 360 nm and then heated at temperatures of500° C. or more or, in some embodiments, 550° C. or more, for a periodranging from about 0.5 hours to about 8 hours, about 1 hour to about 8hours, about 1 hour to about 7 hours, about 1 hour to about 6 hours,about 0.5 hours to about 7 hours, about 0.5 hours to about 6 hours,about 2 hour to about 6 hours, or about 1 hour to about 5 hours, thenegatively photosensitive lithium zinc aluminosilicate glass issubstantially free of crystalline material of sufficient size (<10 nm)that are detectable by x-ray powder diffraction techniques that areknown in the art and routinely used to determine crystal size.

In some embodiments, the negatively photosensitive lithium zincaluminosilicate glass comprises: from about 60 wt % to about 80 wt %SiO₂ (i.e., 60 wt %≤SiO₂≤80 wt %); from about 3 wt % to about 12 wt %Al₂O₃ (i.e., 3 wt %≤Al₂O₃≤12 wt %); from about 2 wt % to about 10 wt %Li₂O (i.e., 2 wt %≤Li₂O≤10 wt %); from 0 wt % to about 5 wt % K₂O (i.e.,0 wt %≤K₂O≤5 wt %); from greater than 0 wt % to about 10 wt % F⁻ (i.e.,0 wt %<F⁻≤10 wt %); from greater than 0 wt % to about 2 wt % CeO₂ (i.e.,0 wt %<CeO₂≤2 wt %); from greater than 0 wt % to about 2 wt % Ag (i.e.,0 wt %<Ag≤2 wt %); and from greater than 0 wt % to about 10 wt % ZnO(i.e., 0 wt %<ZnO≤10 wt %).

In some embodiments, the negatively photosensitive lithium zincaluminosilicate glass comprises: from about 66 wt % to about 76 wt %SiO₂ (i.e., 66 wt %≤SiO₂≤76 wt %); from about 5 wt % to about 9 wt %Al₂O₃ (i.e., 5 wt %≤Al₂O₃≤9 wt %); from about 5 wt % to about 8 wt %Li₂O (i.e., 5 wt %≤Li₂O≤8 wt %); from greater than 0 wt % to about 1 wt% K₂O (i.e., 0 wt %<K₂O≤1 wt %); from greater than 0 wt % to about 6 wt% F⁻ (i.e., 0 wt %<F⁻≤6 wt %); from greater than 0 wt % to about 0.1 wt% CeO₂ (i.e., 0 wt %<CeO₂≤0.1 wt %); from greater than 0 wt % to about0.05 wt % Ag (i.e., 0 wt %<Ag≤0.05 wt %); and from about 6 wt % to about8 wt % ZnO (i.e., 6 wt %≤ZnO≤8 wt %).

In some embodiments, the negatively photosensitive lithium zincaluminosilicate glass may comprise from about 6 wt % to about 8 wt %Li₂O (i.e., 6 wt %≤Li₂O≤8 wt %). In some embodiments, the photosensitivelithium zinc aluminosilicate glass may comprise from about 0.5 wt % toabout 1 wt % K₂O (i.e., 0.5 wt %≤K₂O≤1 wt %). In some embodiments, thephotosensitive lithium zinc aluminosilicate glass may comprise fromabout 0.03 wt % to about 0.09 wt % CeO₂ (i.e., 0.03 wt %≤CeO₂≤0.09 wt%). In some embodiments, the photosensitive lithium zinc aluminosilicateglass may comprise from greater than 0 wt % to about 0.03 wt % Ag (i.e.,0 wt %<Ag≤0.03 wt %). In some embodiments, the photosensitive lithiumzinc aluminosilicate glass may comprise from about 2 wt % to about 4 wt% F⁻ (i.e., 2 wt %≤F⁻≤4 wt %) or from about 2 wt % to about 3.5 wt % F⁻(i.e., 2 wt %≤F⁻≤3.5 wt %). In some embodiments, the photosensitivelithium zinc aluminosilicate glass may comprise up to about 1.5 wt % Br⁻(i.e., 0 wt %≤Br⁻≤4 wt %), or from about 0.3 wt % to about 1.5 wt % Br⁻(i.e., 0.3 wt %≤Br⁻≤1.5 wt %), or from about 0.3 wt % to about 1.3 wt %Br⁻ (i.e., 0.3 wt %≤Br⁻≤1.3 wt %). In some embodiments, the glass isfree of bromine.

In some embodiments, the negatively photosensitive lithium zincaluminosilicate glass may include up to about 0.5, 0.4, 0.3, 0.2, or 0.1wt % Na₂O (i.e., 0 wt %≤Na₂O≤0.5 wt %) and, in some embodiments, is freeof Na₂O. In some embodiments, the photosensitive lithium zincaluminosilicate glass is free of at least one of MgO, P₂O₅, TiO₂, andZrO₂. Non-limiting examples of these negatively photosensitive lithiumzinc aluminosilicate glasses are listed in Table 1. Exposure to UVradiation followed by heat treatment at 500° C. or more or, in someembodiments, 550° C. or more leaves the exposed region clear and thesurrounding unexposed regions, in some embodiments, hazy or evenopalized.

TABLE 1 Compositions of examples of negatively photosensitive lithiumzinc aluminosilicate glasses. Example 1 2 3 4 5 6 Wt % Wt % Wt % Wt % Wt% Wt % SiO₂ 66.9 66.9 66.9 66.9 66.9 66.9 Na₂O 0 0 0 0 0 0 K₂O 0.75 0.750.75 0.75 0.75 0.75 ZnO 6.5 6.5 6.5 6.5 6.5 6.5 Br⁻ 1.26 0.63 0.32 1.260.63 0.32 Al₂O₃ 6.5 6.5 6.5 6.5 6.5 6.5 CeO₂ 0.037 0.037 0.037 0.0370.037 0.074 Ag 0.03 0.03 0.03 0.03 0.03 0.03 Li₂O 6.0 6.0 6.0 6.0 6.06.0 MgO 0 0 0 0 0 0 F⁻ 3.0 3.0 3.0 2.0 2.0 2.0 Example 7 8 9 10 11 12 1314 15 Wt % Wt % Wt % Wt % Wt % Wt % Wt % Wt % Wt % SiO₂ 74.17 75.0575.93 74.44 75.01 75.68 73.35 74.21 75.08 Na₂O 0.76 0.77 0.78 0.76 0.770.78 0.75 0.76 0.77 K₂O 6.5 6.5 6.5 6.5 6.5 6.5 7.14 7.23 7.31 ZnO 0.700.70 0.71 0.70 0.70 0.71 0.69 0.70 0.71 Br⁻ 74.17 75.05 75.93 74.4475.01 75.68 8.63 7.08 5.50 Al₂O₃ 8.72 7.16 5.56 7.09 7.16 7.22 0.04 0.040.04 CeO₂ 0.04 0.04 0.04 0.04 0.08 0.04 0.03 0.03 0.03 Ag 0.03 0.03 0.030.03 0.03 0.03 6.06 6.61 7.18 Li₂O 6.12 6.68 7.26 6.14 6.68 7.23 0.030.03 0.02 Na₂O 0.03 0.03 0.03 0.03 0.03 0.03 2.21 3.31 3.35 F⁻ 2.21 2.232.26 2.21 2.23 2.25 73.35 74.21 75.08

In other embodiments, the lithium zinc aluminosilicate glass ispositively photosensitive; i.e., a region of the material, exposed toultraviolet radiation having a wavelength in a range from about 248 nmto about 360 nm and later heat treated separately at a first temperatureand at a second temperature becomes opalized or translucent, while theunexposed remainder of the material remains clear following such heattreatments. The positively photosensitive lithium zinc aluminosilicateglass may, in some embodiments, be obtained by altering the compositionof the negatively photosensitive glass-ceramic or precursor glass,described hereinabove and subjecting the precursor glass to anadditional heat treatment.

In some embodiments, the positively photosensitive lithium zincaluminosilicate glass comprises: from about 65 wt % to about 80 wt %SiO₂ (65 wt %≤SiO₂≤80 wt %); up to about 1 wt % K₂O (0 wt %≤K₂O≤1 wt %);from about 3 wt % to about 12 wt % ZnO (3 wt %≤ZnO≤12 wt %); up to about10 wt % Br⁻ (0 wt %≤Br⁻≤10 wt %); from about 5 wt % to about 16 wt %Al₂O₃ (5 wt %≤Al₂O₃≤16 wt %); from greater than 0 wt % to about 2 wt %CeO₂ (0 wt %≤CeO₂≤2 wt %); from greater than 0 wt % to about 2 wt % Ag(0 wt %<Ag≤2 wt %); from about 2 wt % to about 14 wt % Li₂O (2 wt%≤Li₂O≤14 wt %); up to about 1 wt % Na₂O (0 wt %≤Na₂O≤1 wt %); fromabout 0 wt % to about 5 wt % F⁻ (0 wt %≤F⁻≤5 wt %); and up to about 8 wt% ZrO₂ (0 wt %≤ZrO₂≤8 wt %).

In some embodiments, the positively photosensitive lithium zincaluminosilicate glass comprises: from about 68 wt % to about 78 wt %SiO₂ (68 wt %≤SiO₂≤78 wt %); up to about 1 wt % K₂O (0 wt %≤K₂O≤1 wt %);from about 5 wt % to about 10 wt % ZnO (5 wt %≤ZnO≤10 wt %); up to about10 wt % Br⁻ (0 wt %≤Br⁻≤10 wt %); from about 5 wt % to about 14 wt %Al₂O₃ (5 wt %≤Al₂O₃≤14 wt %); from about 0.01 wt % to about 0.07 wt %CeO₂ (0.01 wt %≤CeO₂≤0.07 wt %); from about 0.01 wt % to about 0.05 wt %Ag (0.01 wt %≤Ag≤0.05 wt %); from about 5 wt % to about 10 wt % Li₂O (5wt %≤Li₂O≤10 wt %); up to about 1 wt % Na₂O (0 wt %≤Na₂O≤1 wt %); fromabout 0 wt % to about 3 wt % F⁻ (0 wt %≤F⁻≤3 wt %); and up to about 5 wt% ZrO₂ (0 wt %≤ZrO₂≤5 wt %).

In some embodiments, the positively photosensitive lithium zincaluminosilicate precursor glass may be produced by adding ZrO₂ to thenegatively photosensitive lithium zinc aluminosilicate composition.Non-limiting examples of these glasses are listed in Table 2 below.Example 16 in Table 2 is an exemplary composition of the photonegativeglass ceramic and glass. In these embodiments, the positivelyphotosensitive lithium zinc aluminosilicate glass comprises: from about72 wt % to about 76 wt % SiO₂ (72 wt %≤SiO₂≤76 wt %); from about 0.5 wt% to about 1 wt % K₂O (0.5 wt %≤K₂O≤1 wt %); from about 5 wt % to about7 wt % ZnO (5 wt %≤ZnO≤7 wt %); from about 0.5 wt % to about 0.8 wt %Br⁻ (0.5 wt %≤Br⁻≤0.8 wt %); from about 6 wt % to about 8 wt % Al₂O₃ (6wt %≤Al₂O₃≤8 wt %); from about 0.01 wt % to about 0.04 wt % CeO₂ (0.01wt %≤CeO₂≤0.04 wt %); from about 0.03 wt % to about 0.05 wt % Ag (0.03wt %≤Ag≤0.05 wt %); from about 6 wt % to about 8 wt % Li₂O (6 wt%≤Li₂O≤8 wt %); up to about 0.05 wt % Na₂O (0 wt %≤Na₂O≤0.05 wt %); fromabout 2 wt % to about 3 wt % F⁻ (2 wt %≤F⁻≤3 wt %); and from about 0.5wt % to about 5 wt % ZrO₂ (0.5 wt %≤ZrO₂≤5 wt %).

FIG. 1 is a photograph of samples in which ZrO₂ was added to thenegatively photosensitive lithium zinc aluminosilicate precursor glasscomposition. The resulting glasses are positively photosensitive, withthe opalized ceramic phase present in those portions of the samples thatwere exposed to UV radiation and a lithium zinc aluminosilicate glassphase present in those portions of the samples that were not exposed toUV radiation. Samples A and B each have composition 19 (containing 2.92wt % ZrO₂) and samples C, D, and E each have composition 20 (containing3.85 wt % ZrO₂) listed in Table 2. Heat treatment times and temperaturesthat were used to form the lithium-based glass ceramics in examples 19and 20 are listed in Table 2A. Exposed portions 110 of samples A-E inFIG. 1 are opalized while unexposed portions 120 remain clear. X-Raydiffraction (XRD) analysis of the opalized material indicates thepresence of a virgilite Li-aluminosilicate phase. FIG. 2 is a XRDpattern obtained for an opalized portion of a sample having composition18 that was exposed to UV radiation, subsequently heat treated first at575° C. for two hours, cooled to room temperature, and then heat treatedagain at 575° C. for two hours. The XRD pattern shows that the dominantphase has the stuffed β-quartz Li-aluminosilicate (virgiliteLi_(x)Al_(x)Si_(3-x)O₈) crystal structure.

TABLE 2 Compositions of positively photosensitive lithium zincaluminosilicate precursor glasses in which ZrO₂ was added to anegatively photosensitive lithium zinc aluminosilicate glasscomposition. Example 16 17 18 19 20 Wt % Wt % Wt % Wt % Wt % SiO₂ 75.6875.04 74.19 73.46 72.76 K₂O 0.77 0.77 0.76 0.76 0.76 ZnO 6.04 5.99 5.915.85 5.80 Br⁻ 0.71 0.57 0.69 0.69 0.68 Al₂O₃ 7.22 7.15 7.09 7.01 6.94CeO₂ 0.03 0.03 0.03 0.03 0.03 Ag 0.04 0.04 0.04 0.04 0.04 Li₂O 7.23 7.177.09 7.02 6.95 Na₂O 0.03 0.03 0.03 0.03 0.03 F⁻ 2.25 2.23 2.21 2.18 2.16ZrO₂ 0.00 0.99 1.96 2.92 3.85

TABLE 2A Heat treatment times and temperatures for glass ceramic samplesshown in FIG. 1. Example/ First heat Second heat FIG. 1 compositiontreatment treatment A 20 2 hours at 550° 2 hours at 650° B 20 2 hours at550° 2 hours at 600° C 19 2 hours at 675° 2 hours at 675° D 19 2 hoursat 675° 2 hours at 675° E 19 2 hours at 650° 2 hours at 650°

In other embodiments, the positively photosensitive lithium zincaluminosilicate precursor glass is produced by increasing the aluminacontent relative to that of SiO₂ in the negatively photosensitivelithium aluminosilicate composition. In these embodiments, thepositively photosensitive precursor glass comprises: from about 68 wt %to about 76 wt % SiO₂ (68 wt %≤SiO₂≤76 wt %); from about 0.5 wt % toabout 1 wt % K₂O (0.5 wt %≤K₂O≤1 wt %); from about 5 wt % to about 8 wt% ZnO (5 wt %≤ZnO≤8 wt %); from about 0.5 wt % to about 1.0 wt % Br⁻(0.5 wt %≤Br⁻≤1.0 wt %); from about 7 wt % to about 14 wt % Al₂O₃ (7 wt%≤Al₂O₃≤12 wt %); from about 0.01 wt % to about 0.07 wt % CeO₂ (0.01 wt%≤CeO₂≤0.07 wt %); from about 0.03 wt % to about 0.05 wt % Ag (0.03 wt%≤Ag≤0.05 wt %); from about 7 wt % to about 9 wt % Li₂O (7 wt %≤Li₂O≤9wt %); up to about 0.05 wt % Na₂O (0 wt %≤Na₂O≤0.05 wt %); and fromabout 2 wt % to about 3 wt % F⁻ (2 wt %≤F⁻≤3 wt %). Non-limitingexamples of these glasses and glass-ceramics are listed in Table 3below. The alumina content in examples 21 and 22 were increased by 2 wt% and 4 wt %, respectively, relative to the composition of referenceexample 16, listed in Table 1. Example 21 was first heated at 575° C.for two hours and then cooled to room temperature (about 25° C.) andlater heated at 575° C. for two hours, whereas example 22 was firstheated at 550° C. for two hours and then cooled to room temperature andlater heated at 575° C. for two hours. FIG. 3 is a photograph of samplesof examples 21 (F in FIG. 3) and 22 (G in FIG. 3) following irradiationand heat treatments. Both samples have opalized regions 110—and, insample G, 112 and 114—where exposed to UV radiation. The XRD patternobtained for example 22/sample G indicates that the major phase in theopalized regions has the “stuffed β-quartz” lithium-aluminosilicate(virgilite) Li_(x)Al_(x)Si_(3-x)O₈ crystal structure.

TABLE 3 Compositions of positively photosensitive lithium zincaluminosilicate precursor glasses in which alumina content is increasedrelative to that of SiO₂. Example 21 22 23 24 25 26 Wt % Wt % Wt % Wt %Wt % Wt % SiO₂ 73.89 72.14 73.80 71.98 70.11 68.31 K₂O 0.77 0.76 0.780.81 0.87 0.92 ZnO 5.99 5.94 6.56 7.02 7.46 7.93 Br⁻ 0.71 0.70 0.72 0.760.82 0.87 Al₂O₃ 9.14 11.04 7.85 8.41 9.02 9.51 CeO₂ 0.03 0.03 0.03 0.030.06 0.06 Ag 0.04 0.04 0.04 0.04 0.04 0.04 Li₂O 7.17 7.11 7.77 8.32 8.849.39 Na₂O 0.03 0.03 0.03 0.03 0.03 0.03 F⁻ 2.23 2.21 2.42 2.59 2.75 2.93ZrO₂ 0.00 0.00

While ZnO is a constituent of the negatively photosensitiveglass-ceramic and precursor glasses, a positively photosensitiveglass-ceramic and precursor glass may be obtained by increasing the ZnOconcentration relative to the alumina and silica content in thenegatively photosensitive lithium aluminosilicate composition. In theseembodiments, the positively photosensitive glass precursor glasscomprises: from about 68 wt % to about 77 wt % SiO₂ (68 wt %≤SiO₂≤77 wt%); from about 0.5 wt % to about 1 wt % K₂O (0.5 wt %≤K₂O≤1 wt %); fromabout 6 wt % to about 10 wt % ZnO (6 wt %≤ZnO≤10 wt %); from about 0.5wt % to about 1.0 wt % Br⁻ (0.5 wt %≤Br⁻≤1 wt %); from about 7 wt % toabout 10 wt % Al₂O₃ (7 wt %≤Al₂O₃≤10 wt %); from about 0.02 wt % toabout 0.05 wt % CeO₂ (0.02 wt %≤CeO₂≤0.05 wt %); from about 0.02 wt % toabout 0.05 wt % Ag (0.03 wt %≤Ag≤0.05 wt %); from about 7 wt % to about10 wt % Li₂O (7 wt %≤Li₂O≤10 wt %); up to about 0.05 wt % Na₂O (0 wt%≤Na₂O≤0.05 wt %); from about 1 wt % to about 3 wt % F⁻ (1 wt %≤F⁻≤3 wt%), and up to about 4 wt % ZrO₂ (0 wt %≤ZrO₂≤4 wt %). Compositions ofnon-limiting examples of these positively photosensitive lithium zincaluminosilicate glasses are listed in Table 4 below. The glass-ceramicmay, in some embodiments, be obtained by first exposing the positivelyphotosensitive precursor glass to ultraviolet light followed by a firstheat treatment at about 575° C. for two hours, then cooling theprecursor glass to room temperature (about 25° C.) and later heating theprecursor glass at about 575° C. for two hours to form the glassceramic. FIG. 4 is a photograph of samples of examples 28 (H in FIG. 4)and 30 (I in FIG. 4) following irradiation and heat treatments. Bothsamples have opalized region 110—and, in sample H, 114, and in sample I,112—where the material was exposed to UV radiation. The XRD patternobtained for examples 30/sample I (FIG. 4) indicates that the majorphase in the opalized regions has the “stuffed β-quartz”lithium-aluminosilicate (virgilite) Li_(x)Al_(x)Si_(3-x)O₈ crystalstructure.

TABLE 4 Compositions of positively photosensitive lithium zincaluminosilicate precursor glasses in which the ZnO concentration isincreased relative to the alumina and SiO₂ content. Example TVY TVZ TWATWB TWC Wt % Wt % Wt % Wt % Wt % SiO₂ 73.84 73.19 72.89 76.20 70.97 K₂O0.77 0.78 0.79 0.79 0.74 ZnO 6.56 9.05 7.45 6.16 6.31 Br⁻ 0.72 0.71 0.700.70 0.69 Al₂O₃ 7.86 7.02 8.96 7.36 7.55 CeO₂ 0.04 0.04 0.04 0.04 0.04Ag 0.03 0.03 0.03 0.03 0.03 Li₂O 7.77 7.77 8.32 8.84 9.39 Na₂O 0.03 0.030.03 0.03 0.03 F⁻ 2.25 2.18 2.17 1.84 2.33 ZrO₂ 0 0 0 0 3.84

In other embodiments, the positively photosensitive lithium zincaluminosilicate precursor glasses may be obtained by replacing fluorinewith bromine. In such embodiments, the precursor glass may comprise upto about 10 wt % or, in some embodiments, up to about 1 wt % Br. Inthese embodiments, the positively photosensitive lithium zincaluminosilicate precursor glass may comprise: from about 70 wt % toabout 78 wt % SiO₂ (70 wt %≤SiO₂≤78 wt %); from about 0.5 wt % to about1 wt % K₂O (0.5 wt %≤K₂O≤1 wt %); from about 5 wt % to about 7 wt % ZnO(5 wt %≤ZnO≤7 wt %); from about 0 wt % to about 10 wt % Br⁻ (0.5 wt%≤Br⁻≤10 wt %); from about 6 wt % to about 8 wt % Al₂O₃ (6 wt %≤Al₂O₃≤8wt %); from about 0.02 wt % to about 0.05 wt % CeO₂ (0.02 wt %≤CeO₂≤0.05wt %); from about 0.02 wt % to about 0.05 wt % Ag (0.02 wt %≤Ag≤0.05 wt%); from about 6 wt % to about 8 wt % Li₂O (6 wt %≤Li₂O≤8 wt %); up toabout 1 wt % Na₂O (0 wt %≤Na₂O≤1 wt %); and from 0 wt % to about 3 wt %F⁻ (0 wt %≤F⁻≤3 wt %). Non-limiting examples of these glasses andglass-ceramics are listed in Table 5 below. The XRD patterns obtainedfor samples having the composition listed for example 34 indicate thatthe major phase in the opalized regions has the “stuffed β-quartz”lithium-aluminosilicate (virgilite) Li_(x)Al_(x)Si_(3-x)O₈ crystalstructure. Although these samples were heat treated at differenttemperatures, no discernable difference in the XRD data was observed.

TABLE 5 Compositions of positively photosensitive lithium zincaluminosilicate precursor glasses in which fluorine is replaced bybromine. Example 32 33 34 35 36 37 38 Wt % Wt % Wt % Wt % Wt % Wt % Wt %SiO₂ 77.98 77.36 76.75 73.00 72.45 71.91 70.58 K₂O 0.80 0.79 0.79 0.750.74 0.74 0.72 ZnO 6.21 6.16 6.11 5.82 5.77 5.73 5.62 Br⁻ 0 0 0 6.406.35 6.30 9.50 Al₂O₃ 7.44 7.38 7.32 6.96 6.91 6.86 6.73 CeO₂ 0.04 0.040.04 0.04 0.04 0.04 0.04 Ag 0.03 0.03 0.03 0.03 0.03 0.03 0.03 Li₂O 7.457.39 7.33 6.98 6.92 6.87 6.74 Na₂O 0.80 0.79 0.79 0.75 0.74 0.03 0.03 F⁻0 0.78 1.59 0 0.75 1.49 0

In another aspect, a composite glass article comprising a lithium-basedglass ceramic and a photosensitive lithium zinc aluminosilicate glass isprovided. The composite glass article comprises a first region and asecond region. The first region comprises a lithium-based glass ceramiccomprising a ceramic phase and a residual glass phase. The ceramic phasecomprises a lithium aluminosilicate (LAS) phase having a lithiumaluminosilicate stuffed β-quartz structure, such as describedhereinabove. In some embodiments, the lithium-based glass ceramic isfree of at least one of Na₂O, MgO, P₂O₅, TiO₂, ZrO₂, or bromine. In someembodiments, the LAS phase comprises at least about 50 volume percent ofthe glass ceramic region.

The second region comprises a lithium zinc aluminosilicate glass that isphotosensitive to ultraviolet radiation having a wavelength in a rangefrom about 248 nm to about 360 nm, such as those described hereinabove.The lithium zinc aluminosilicate glass comprises at least onesensitizing agent and at least one nucleating agent. In someembodiments, the at least one sensitizing agent may include, but is notlimited to, at least one of silver or cerium. The at least onenucleating agent may include, but is not limited to, silver and/or atleast one halogen or halide. In some embodiments, the at least onenucleating agent comprises at least one of fluorine, chlorine, orbromine. In particular embodiments, the at least one nucleating agentcomprises fluorine or bromine.

In some embodiments, the first region is opaque or translucent. In someembodiments, the lithium zinc aluminosilicate glass is transparent.

In some embodiments, the lithium zinc aluminosilicate glass isnegatively photosensitive with respect to the ultraviolet radiation;i.e., a region of the glass exposed to ultraviolet radiation andsubsequently heat treated or cerammed remains clear, while the remainderof the material that is not exposed to, or shielded from, such radiationand heat treated becomes opalized or translucent when heat treated orcerammed. In those embodiments in which the second region comprises anegatively photosensitive lithium zinc aluminosilicate glass, the firstregion, which comprises the lithium-based glass ceramic, is not exposed(i.e., is “unexposed”) to UV radiation.

In some embodiments, the negatively photosensitive lithium zincaluminosilicate glass comprises: from about 66 wt % to about 76 wt %SiO₂ (i.e., 66 wt %≤SiO₂ 76 wt %); from about 5 wt % to about 9 wt %Al₂O₃ (i.e., 5 wt %≤Al₂O₃≤9 wt %); from about 5 wt % to about 8 wt %Li₂O (i.e., 5 wt %≤Li₂O≤8 wt %); from greater than 0 wt % to about 1 wt% K₂O (i.e., 0 wt %<K₂O≤1 wt %); from greater than 0 wt % to about 6 wt% F⁻ (i.e., 0 wt %≤F⁻≤6 wt %); from greater than 0 wt % to about 0.1 wt% CeO₂ (i.e., 0 wt %<CeO₂≤0.1 wt %); from greater than 0 wt % to about0.05 wt % Ag (i.e., 0 wt %<Ag≤0.05 wt %); and from about 6 wt % to about8 wt % ZnO (i.e., 6 wt %≤ZnO≤8 wt %).

In other embodiments, the second region comprises a positivelyphotosensitive lithium zinc aluminosilicate glass; i.e., a region of theglass, exposed to ultraviolet radiation having a wavelength in a rangefrom about 248 nm to about 360 nm becomes opalized or translucent whenlater heat treated separately at a first temperature and at a secondtemperature, while the unexposed remainder of the material remains clearfollowing such heat treatments. These positively photosensitive glasseshave been previously described hereinabove, and comprise: from about 68wt % to about 78 wt % SiO₂ (68 wt %≤SiO₂≤78 wt %); up to about 1 wt %K₂O (0 wt %≤K₂O≤1 wt %); from about 5 wt % to about 10 wt % ZnO (4 wt%≤ZnO≤8 wt %); up to about 10 wt % Br⁻ (0 wt %≤Br⁻≤10 wt %); from about5 wt % to about 14 wt % Al₂O₃ (5 wt %≤Al₂O₃≤12 wt %); from about 0.01 wt% to about 0.07 wt % CeO₂ (0.01 wt %≤CeO₂≤0.07 wt %); from about 0.01 wt% to about 0.05 wt % Ag (0.01 wt %≤Ag≤0.05 wt %); from about 5 wt % toabout 10 wt % Li₂O (5 wt %≤Li₂O≤10 wt %); up to about 1 wt % Na₂O (0 wt%≤Na₂O≤1 wt %); from about 0 wt % to about 3 wt % F⁻ (0 wt %≤F⁻≤3 wt %);and up to about 5 wt % ZrO₂ (0 wt %≤ZrO₂≤5 wt %).

In some embodiments, the positively photosensitive lithium zincaluminosilicate glass comprises: from about 72 wt % to about 76 wt %SiO₂ (72 wt %≤SiO₂≤76 wt %); from about 0.5 wt % to about 1 wt % K₂O(0.5 wt %≤K₂O≤1 wt %); from about 5 wt % to about 7 wt % ZnO (5 wt%≤ZnO≤7 wt %); from about 0.5 wt % to about 0.8 wt % Br⁻ (0.5 wt%≤Br⁻≤0.8 wt %); from about 6 wt % to about 8 wt % Al₂O₃ (6 wt %≤Al₂O₃≤8wt %); from about 0.01 wt % to about 0.04 wt % CeO₂ (0.01 wt %≤CeO₂≤0.04wt %); from about 0.03 wt % to about 0.05 wt % Ag (0.03 wt %≤Ag≤0.05 wt%); from about 6 wt % to about 8 wt % Li₂O (6 wt %≤Li₂O≤8 wt %); up toabout 0.05 wt % Na₂O (0 wt %≤Na₂O≤0.05 wt %); from about 2 wt % to about3 wt % F⁻ (2 wt %≤F⁻≤3 wt %); and from about 0.5 wt % to about 5 wt %ZrO₂ (0.5 wt %≤ZrO₂≤5 wt %).

In some embodiments, the positively photosensitive lithium zincaluminosilicate glass comprises: from about 68 wt % to about 76 wt %SiO₂ (68 wt %≤SiO₂≤76 wt %); from about 0.5 wt % to about 1 wt % K₂O(0.5 wt %≤K₂O≤1 wt %); from about 5 wt % to about 8 wt % ZnO (5 wt%≤ZnO≤8 wt %); from about 0.5 wt % to about 1.0 wt % Br⁻ (0.5 wt%≤Br⁻≤1.0 wt %); from about 7 wt % to about 14 wt % Al₂O₃ (7 wt%≤Al₂O₃≤12 wt %); from about 0.01 wt % to about 0.07 wt % CeO₂ (0.01 wt%≤CeO₂≤0.07 wt %); from about 0.03 wt % to about 0.05 wt % Ag (0.03 wt%≤Ag≤0.05 wt %); from about 7 wt % to about 9 wt % Li₂O (7 wt %≤Li₂O≤9wt %); up to about 0.05 wt % Na₂O (0 wt % Na₂O≤≤0.05 wt %); and fromabout 2 wt % to about 3 wt % F⁻ (2 wt %≤F⁻≤3 wt %).

In some embodiments, the positively photosensitive lithium zincaluminosilicate glass comprises: from about 68 wt % to about 77 wt %SiO₂ (68 wt %≤SiO₂≤77 wt %); from about 0.5 wt % to about 1 wt % K₂O(0.5 wt %≤K₂O≤1 wt %); from about 6 wt % to about 10 wt % ZnO (6 wt%≤ZnO≤10 wt %); from about 0.5 wt % to about 1.0 wt % Br⁻ (0.5 wt%≤Br⁻≤1 wt %); from about 7 wt % to about 10 wt % Al₂O₃ (7 wt %≤Al₂O₃≤10wt %); from about 0.02 wt % to about 0.05 wt % CeO₂ (0.02 wt %≤CeO₂≤0.05wt %); from about 0.02 wt % to about 0.05 wt % Ag (0.03 wt %≤Ag≤0.05 wt%); from about 7 wt % to about 10 wt % Li₂O (7 wt %≤Li₂O≤10 wt %); up toabout 0.05 wt % Na₂O (0 wt %≤Na₂O≤0.05 wt %); from about 1 wt % to about3 wt % F⁻ (1 wt %≤F⁻≤3 wt %), and up to about 4 wt % ZrO₂ (0 wt %≤ZrO₂≤4wt %).

In some embodiments, the positively photosensitive lithium zincaluminosilicate glass comprises: from about 70 wt % to about 78 wt %SiO₂ (70 wt %≤SiO₂≤78 wt %); from about 0.5 wt % to about 1 wt % K₂O(0.5 wt %≤K₂O≤1 wt %); from about 5 wt % to about 7 wt % ZnO (5 wt%≤ZnO≤7 wt %); from about 0 wt % to about 10 wt % Br⁻ (0.5 wt %≤Br⁻≤10wt %); from about 6 wt % to about 8 wt % Al₂O₃ (6 wt %≤Al₂O₃≤8 wt %);from about 0.02 wt % to about 0.05 wt % CeO₂ (0.02 wt %≤CeO₂≤0.05 wt %);from about 0.02 wt % to about 0.05 wt % Ag (0.02 wt %≤Ag≤0.05 wt %);from about 6 wt % to about 8 wt % Li₂O (6 wt %≤Li₂O≤8 wt %); up to about1 wt % Na₂O (0 wt %≤Na₂O≤1 wt %); and from 0 wt % to about 3 wt % F⁻ (0wt %≤F⁻≤3 wt %).

In some embodiments, the first region (the lithium-based glass ceramic)and the second region (the lithium zinc aluminosilicate glass) of thecomposite glass articles described herein may be randomly dispersedthroughout the composite glass article. In other embodiments, the firstregion and second region are spatially separate from each other.

In some embodiments, the first region (the lithium-based glass ceramic)and the second region (the lithium zinc aluminosilicate glass) of thecomposite glass articles described herein may be arranged in an array.The array may, in some embodiments, be a regular, repeated pattern,which may be either short range (i.e., having/extending in a dimensionof up to about 1 mm or less) or long range (i.e., having adimension/extending in a dimension of greater than 1 mm). Such an arraymay be formed by selectively irradiating portions of the precursor glasswith UV light in a predetermined pattern, or by shielding a portion ofthe precursor glass from the UV light.

In some embodiments, the lithium-based glass ceramic has a thermalexpansion ΔL₁/L₁ and the lithium zinc aluminosilicate glass has athermal expansion ΔL₂/L₂ measured between room temperature and a secondtemperature T, wherein 25° C.≤T≤300° C., where ΔL_(i) is the change indimension L_(i) of the lithium-based glass ceramic and the lithium zincaluminosilicate glass over the temperature range measured. This thermalexpansion differential places the lithium zinc aluminosilicate glass intension and the lithium-based glass ceramic in compression at theboundary between the glass and ceramic phases, thereby increasing themechanical strength of the composite glass article.

Thermal expansion of the lithium-based glass ceramic and the lithiumzinc aluminosilicate glass of the composite glass article are plotted asfunction of temperature in FIGS. 5A and 5B, respectively. As seen inFIGS. 5A and 5B, the lithium-based glass ceramic undergoes a 0.6%decrease in volume as it cools from the thermal development temperatureof 600° C., whereas the lithium zinc aluminosilicate glass undergoes a0.3% decrease in volume upon cooling from the thermal developmenttemperature. Thus volume of the lithium-based glass ceramic experiencesa 50% greater volume decrease relative to the lithium zincaluminosilicate glass, which results in a build-up of compressive stressin the lithium-based glass ceramic and tensile stress in the lithiumzinc aluminosilicate glass at the boundary of the glass ceramic/glassinterface. The nature of the compressive and tensile stresses thatdevelop under this condition provides a stress region that is capable ofdeflecting a propagating crack.

The induced stress between the lithium-based glass ceramic and thelithium zinc aluminosilicate glass may be observed in the resultingoptical birefringence and on the microscopic level as well. FIGS. 6A and6B are microscopic images of a composite glass article undernon-polarized light and polarized light, respectively. Composite glassarticle 600 comprises a lithium-based glass ceramic 620 and a lithiumzinc aluminosilicate glass 610. Stress 614 at the interface between thelithium-based glass ceramic 620 and the lithium zinc aluminosilicateglass 610, which is induced by the photo-elastic effect, is visibleunder polarized light (FIG. 6B).

FIG. 7 is a photograph showing the internal stress produced by thepatterned composite glass article comprising the negativelyphotosensitive lithium zinc aluminosilicate glass and the lithium-basedglass ceramic described herein. The sample is viewed between crossedpolarizers, and the magnitude of the stress is seen through thephoto-elastic effect (i.e., stress-induced birefringence). The compositeglass article comprises lithium zinc aluminosilicate glass 710surrounded by the lithium-based glass ceramic 720. The negativelyphotosensitive lithium zinc aluminosilicate glass in composite glassarticle 700 has the composition of example 16 (Table 2). When viewedbetween crossed polarizers, stress patterns 715 appear in the glassregions 710 surrounded by the glass ceramic region 720.

By introducing compressive and tensile stress at the boundary interfaceof the glass-ceramic and lithium zinc aluminosilicate glass, thepatterned composite glass articles described herein may be used tofrustrate crack propagation from the edges of such an article. Such anarticle is schematically shown in FIG. 8. Composite glass article 805comprises a first region 815 comprising a lithium zinc aluminosilicateglass and a second region comprising a lithium-based glass ceramic 815.Both the lithium zinc aluminosilicate glass and the lithium-base glassceramic are described herein. If the lithium zinc aluminosilicate glassis positively photosensitive, a central portion 810 of the precursorglass 800 is not exposed to UV radiation, while a peripheral portion 820of the precursor glass 800 is exposed to UV radiation. Followingexposure to the UV radiation (830 in FIG. 8), the precursor lithium zincaluminosilicate glass is then heated to and held at a first temperaturefor a predetermined period of time and cooled to room temperature (840),and then heated to and held at a second temperature for a predeterminedperiod of time and cooled to room temperature (850) to form thelithium-based glass ceramic and composite glass article 805. Aglass-ceramic is formed in the exposed peripheral portion 820, wherein acompressive stress (815 in FIG. 8) exists within the lithium-based glassceramic and a tensile stress is created in the lithium zincaluminosilicate glass at the interface between the lithium zincaluminosilicate glass and lithium-based glass ceramic. This interfacialstress frustrates the propagation of cracks from the edges of thecomposite glass article 805.

In those instances in which the lithium zinc aluminosilicate glass isnegatively photosensitive, central portion 810 of the precursor glass800 is exposed to UV radiation, while peripheral portion 820 of theprecursor glass 800 is not exposed to UV radiation. Following exposureto the UV radiation (830 in FIG. 8), the precursor lithium zincaluminosilicate glass is then heated to and held at a first temperaturefor a predetermined period of time and cooled to room temperature (845)to form the lithium-based glass ceramic and composite glass article 805.

In another aspect, a method of making the composite glass articledescribed hereinabove from a negatively photosensitive lithium zincaluminosilicate precursor glass (precursor glass) is provided. Thecomposite glass article comprises a lithium zinc aluminosilicate glassand a lithium-based glass ceramic. The lithium-based glass ceramiccomprises a residual glass phase and a ceramic phase comprising astuffed β-quartz lithium-aluminosilicate (virgilite, orLi_(x)Al_(x)Si_(3-x)O₈) crystal structure and, in some embodiments, acrystalline LiF phase. The lithium-based glass ceramic, in someembodiments, may be opalized or translucent.

A flow chart describing the method is shown in FIG. 9. In a first step910 of method 900, a negatively photosensitive lithium zincaluminosilicate precursor glass comprising at least one sensitizingagent and at least one nucleating agent is provided. The precursor glassmay be formed by those means known in the art including down-draw(fusion- or slot-draw), up draw, float methods, casting, molding, or thelike.

In a second step 920, a first region of the negatively photosensitivelithium zinc aluminosilicate precursor glass is exposed to ultravioletradiation having a wavelength in a range from about 248 nm to about 360nm, while a second region of the negatively photosensitive lithium zincaluminosilicate precursor glass is unexposed to the ultravioletradiation. In some embodiments, the first region is irradiated with a UVlaser such as, for example, a 355 nm pulsed laser or the like, or a beamof continuous UV light such as, for example, a 310 nm Hg arc lamp; whilea second region of the precursor glass is not irradiated with (i.e.,unexposed to) the UV radiation. In other embodiments, the second regionof the precursor glass may be shielded from the UV radiation. Suchshielding may include an opaque or reflective film, such as those knownin the art, which is applied to the surface of the second region. Aspreviously described hereinabove, the UV radiation may, in someembodiments, have a wavelength of 355 nm, 10 Hz frequency, and a fluenceof 6.5 W/cm². In some embodiments, the UV laser or beam is rasteredacross at least the portion of the negatively photosensitive lithiumzinc aluminosilicate precursor glass. For example, the precursor glassmay be irradiated for 5 seconds with UV light rastered across thematerial at a rate of 10 mm/sec. In other embodiments, the negativelyphotosensitive lithium zinc aluminosilicate precursor glass may becontinuously irradiated with UV light for a fixed time period (e.g., forabout 1 minute, or for times ranging from about 5 to about 10 seconds).

The UV-exposed negatively photosensitive lithium zinc aluminosilicateprecursor glass is then heated to form the lithium-based glass ceramicin the second region, thereby forming the composite glass article (step930). In some embodiments, the exposed lithium zinc aluminosilicateprecursor glass is heated at a temperature in a range from about 550° C.to about 650° C. for at least about 2 hours. In some embodiments, thecrystalline lithium-aluminosilicate and LiF phases (when present) in thesecond region, which was not exposed to the UV radiation, have crystalsizes of at least as large as the wavelength of visible light (≥400 nm)and thus scatter light and are opalized, rendering the ceramic phaseopaque or translucent. In some embodiments, however, the crystal sizesin the second region are sufficiently small so as to not scatter orappreciably refract light, thus rendering the ceramic phase transparent.

In yet another aspect, a method of making the composite glass articledescribed hereinabove from a positively photosensitive lithium zincaluminosilicate precursor glass (precursor glass) is provided. Thecomposite glass article comprises a lithium zinc aluminosilicate glassand a lithium-based glass ceramic. The lithium-based glass ceramiccomprises a residual glass phase and a ceramic phase comprising astuffed β-quartz lithium-aluminosilicate (virgilite, orLi_(x)Al_(x)Si_(3-x)O₈) crystal structure and, in some embodiments, acrystalline LiF phase. The lithium-based glass ceramic, in someembodiments, may be opalized or translucent.

A flow chart describing the method is shown in FIG. 10. In a first step1010 of method 1000, a positively photosensitive lithium zincaluminosilicate precursor glass comprising at least one sensitizingagent and at least one nucleating agent is provided. The precursor glassmay be formed by those means known in the art including down-draw(fusion- or slot-draw), up draw, float methods, casting, molding, or thelike.

In a second step 1020, a first region of the positively photosensitivelithium zinc aluminosilicate precursor glass is exposed to ultravioletradiation having a wavelength in a range from about 248 nm to about 360nm while a second region of the lithium zinc aluminosilicate glass isunexposed (i.e., not exposed) to the ultraviolet radiation. In someembodiments, the first region is irradiated with a UV laser such as, forexample, a 355 nm pulsed laser or the like, or a beam of continuous UVlight such as, for example, a 310 nm Hg arc lamp; while a second regionof the precursor glass is not irradiated with UV radiation. In otherembodiments, the second region of the precursor glass may be shieldedfrom the UV radiation. Such shielding may include an opaque orreflective film, such as those known in the art, which is applied to thesurface of the second region. As previously described hereinabove, theUV radiation may, in some embodiments, have a wavelength of 355 nm, 10Hz frequency, and 6.5 W/cm² energy. In some embodiments, the UV laser orfocused beam is rastered across at least the portion of the negativelyphotosensitive lithium zinc aluminosilicate precursor glass. Forexample, the precursor glass may be irradiated for 5 seconds with UVlight rastered across the material at a rate of 10 mm/sec. In otherembodiments, the positively photosensitive lithium zinc aluminosilicateprecursor glass may be continuously irradiated with UV light for a fixedtime period (e.g., for about 1 minute, or for times ranging from about 5to about 10 seconds, or, in some embodiments, for up to two hours).

Following exposure to the UV radiation, the lithium zinc aluminosilicateprecursor glass is heated at a first temperature for a firstpredetermined time period to reduce silver using cerium as an opticalintermediate (Step 1030). In some embodiments, the first temperature isin a range from about 550° C. to about 700° C., and the firstpredetermined time period ranges from about 0.5 hours to about 4 hours.The precursor glass is and then cooled to room temperature(approximately 25° C.) (not shown). The exposed precursor glass is thenheated at a second temperature for a second predetermined time period toform a lithium-based glass ceramic in the first region, wherein theglass ceramic comprises a residual glass phase and a ceramic phasecomprising a stuffed β-quartz lithium-aluminosilicate (virgilite, orLi_(x)Al_(x)Si_(3-x)O₈) crystal structure and, in some embodiments, acrystalline LiF phase (Step 1040), and thereby forming the compositeglass article. In some embodiments, the second temperature is in a rangefrom about 500° C. to about 700° C., and the second predetermined timeperiod ranges from about 0.5 hours to about 4 hours. Finally, thecomposite glass article is cooled to room temperature (approximately 25°C.) (not shown).

While typical embodiments have been set forth for the purpose ofillustration, the foregoing description should not be deemed to be alimitation on the scope of the disclosure or appended claims.Accordingly, various modifications, adaptations, and alternatives mayoccur to one skilled in the art without departing from the spirit andscope of the present disclosure or appended claims.

The invention claimed is:
 1. A method of making a composite glassarticle, the composite glass article comprising a lithium zincaluminosilicate glass and a lithium-based glass ceramic, thelithium-based glass ceramic comprising a ceramic phase, the ceramicphase comprising a lithium aluminosilicate phase having a lithiumaluminosilicate b-quartz structure, and residual glass phase, the methodcomprising: a. providing a lithium zinc aluminosilicate precursor glass,the lithium zinc aluminosilicate glass comprising at least onesensitizing agent and at least one nucleating agent, wherein the lithiumzinc aluminosilicate glass is negatively photosensitive; b. exposing afirst region of the lithium zinc aluminosilicate precursor glass toultraviolet radiation having a wavelength in a range from about 248 nmto about 360 nm, while a second region of the lithium zincaluminosilicate precursor glass is unexposed to the ultravioletradiation; c. performing a first heating step of the exposed lithiumzinc aluminosilicate precursor glass at a temperature in a range fromabout 550° C. to about 650° C.; d. cooling the heated exposed lithiumzinc aluminosilicate precursor glass; and e. heating the cooled exposedlithium zinc aluminosilicate precursor glass at a temperature in a rangefrom about 550° C. to about 650° C. to form the lithium-based glassceramic in the second region, thereby forming the composite glassarticle, wherein the lithium zinc aluminosilicate precursor glasscomprises: from about 66 wt % to about 80 wt % SiO₂; from about 3 wt %to about 12 wt % Al₂O₃; from about 2 wt % to about 10 wt % Li₂O; fromgreater than 0 wt % to about 5 wt % K₂O; 1 wt % to 2.93 wt % F—; fromgreater than 0 wt % to about 2 wt % CeO₂; from greater than 0 wt % toabout 2 wt % Ag; and from about 0 wt % to about 10 wt % ZnO.
 2. Themethod of claim 1, wherein the lithium zinc aluminosilicate precursorglass comprises: from about 66 wt % to about 76 wt % SiO₂; from about 5wt % to about 9 wt % Al₂O₃; from about 5 wt % to about 8 wt % Li₂O; fromgreater than 0 wt % to about 1 wt % K₂O; from greater than 2 wt % toabout 2.93 wt % F—; from greater than 0 wt % to about 0.5 wt % CeO₂;from greater than 0 wt % to about 0.5 wt % Ag; and from about 6 wt % toabout 8 wt % ZnO.
 3. The method of claim 1, wherein heating the exposedlithium zinc aluminosilicate precursor glass comprises heating theexposed lithium zinc aluminosilicate glass for at least 2 hours.
 4. Themethod of claim 1, wherein the at least one sensitizing agent comprisesat least one of silver and cerium and the at least one nucleating agentcomprises at least one halogen.
 5. A method of making a composite glassarticle, the composite glass article comprising a lithium zincaluminosilicate glass and a lithium-based glass ceramic, thelithium-based glass ceramic comprising a ceramic phase, the ceramicphase comprising a lithium aluminosilicate phase having a lithiumaluminosilicate β-quartz structure, and residual glass phase, the methodcomprising: a. providing a lithium zinc aluminosilicate precursor glass,the lithium zinc aluminosilicate glass comprising at least onesensitizing agent and at least one nucleating agent, wherein the lithiumzinc aluminosilicate glass is positively photosensitive; b. exposing afirst region of the lithium zinc aluminosilicate precursor glass withultraviolet radiation having a wavelength in a range from about 248 nmto about 360 nm while a second region of the lithium zincaluminosilicate glass is unexposed to the ultraviolet radiation; c.heating the lithium zinc aluminosilicate precursor glass at a firsttemperature in a range from about 550° C. to about 675° C. for a firsttime period to reduce silver present in the lithium zincaluminosilicate; and d. heating the lithium zinc aluminosilicateprecursor glass at a second temperature in a range from about 550° C. toabout 675° C. for a second time period to form the lithium-based glassceramic in the first region, thereby forming the composite glass articlewherein the lithium zinc aluminosilicate precursor glass comprises: fromabout 65 wt % to about 80 wt % SiO₂; from about 0 wt % to about 1 wt %K₂O; from about 3 wt % to about 12 wt % ZnO; up to about 10 wt % Br;from about 5 wt % to about 16 wt % Al₂O₃; from greater than 0 wt % toabout 2 wt % CeO₂; from 0 wt % to about 2 wt % Ag; from about 2 wt % toabout 14 wt % Li₂O; up to about 1 wt % Na₂O; 1 wt % to 2.93 wt % F; andup to about 8 wt % ZrO₂.
 6. The method of claim 5, wherein the firsttime period is in a range from about 0.5 hours to about 4 hours and thesecond time period is in a range from about 0.5 hours to about 4 hours.